Electrospray ionization (ESI) is a commonly used ionization technique for mass spectrometry (MS) in which analyte ions are generated and effectively transported from solution phase to the gas phase. In ESI, analytes in a charged solution are sprayed pneumatically to produce a plume of charged microdroplets. These microdroplets undergo desolvation and coulombic fission events to produce numerous smaller and more concentrated droplets. These microdroplets are the nexus for accelerated chemical reactions.
On-line monitoring experiments have demonstrated that increasing a distance between the sprayer and a mass spectrometer inlet increases a product to starting material ratio. It has been demonstrated that reaction rate acceleration in spray (compared to bulk) for the Pomeranz-Fritsch synthesis of isoquinoline was greater than six orders of magnitude. In a study of the Claisen-Schmidt base-catalyzed condensation, it was shown that acceleration is not simply a result of increased concentration dependence but is strongly influenced by interfacial effects. Successful efforts at milligram scale chemical synthesis using reactions in electrosprayed droplets have been reported.